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Floating islands to protect Lake Hopatcong from algae

Photo by Tracy Klimek/New Jersey Herald Fred Lubnow, with Princeton Hydro, places the plant Golden Alexander into small holes filled with dirt on a floating island made from recycled plastic on Wednesday. It will be placed in Lake Hopatcong’s Ashley Cove.

JEFFERSON — Babylon had its “hanging gardens,” Lake Hopatcong now has its “floating islands.”

While called Floating Wetlands Islands, what was installed Wednesday in Ashley Cove looked more like giant plastic foam rafts, with seedlings popping up.

Within a year, however, the plastic rafts will be almost invisible, covered with native plants happily soaking up phosphorus from the lake’s waters.

That is what’s happening above water, but on the underside of the rafts there’s even more activity, although it won’t be visible, said Fred Lubnow from Princeton Hydro, the specialist who is bringing the floating islands to the lake.

While plants are growing on top of the plastic rafts, their roots dropping through the bottom and into the water. The underside of the raft will become home to naturally occurring microbes that will also feast on the phosphorous in the water.

“There is a study that shows that on each island, the plants take up about 20 percent of the phosphorous and the microbes take up 80 percent,” he said.

Phosphorous is the nutrient in the water that feeds the algae and other noxious weeds found along the shoreline of Lake Hopatcong, the state’s biggest freshwater lake. Algae is the slimy, green growth that dies off each autumn and, over the course of a few years, creates the muck on the bottom of the lake’s many coves.

While phosphorous naturally occurs in combination with other minerals and is an essential to all life, human activity produces an abundance of the chemical. It is used in many products from detergents to fertilizers.

Too much phosphorous in the water leads to an overabundance of algae.

For years now, Lubnow and Princeton Hydro have been working to keep phosphorous out of the lake by shutting off its sources. New Jersey has outlawed detergents and fertilizers containing the element, but human activity — think septic systems — remains a major contributor into the groundwater and eventually into the lake.

Princeton Hydro has designed many projects to capture the phosphorous and other pollutants before they get into the streams that feed the lake.

Lubnow said the area around Ashley Cove needed several permits for such a non-point source structure, taking up both time and money.

The floating island solution requires no such permits, needing only the relatively cheap plastic floats, some plants and a little potting soil.

Funds for the project came through a grant awarded to the Lake Hopatcong Commission and are being implemented by the Lake Hopatcong Foundation. The installation on Wednesday was done with help of volunteers as well as employees from the Lake Hopatcong Foundation, Jefferson Township and Princeton Hydro.

The theory behind the floating islands is to create a place where native plants can get to the phosphorous before the chemical gets close to shore. By putting rafts of plants — the floating wetland islands — farther out from shore, those plants get first chance at the phosphorous that the lake’s natural flow pushes toward the shoreline, reducing the amount that gets to the algae and other plants along the shoreline.

The rafts won’t totally eliminate the lake’s algae but will take up nutrients that otherwise would go to feed the algae.

The two islands created on Wednesday are likely to take in 10 pounds of phosphorous per year.

“It doesn’t sound like much, but one pound of phosphorous can produce about eleven-hundred pounds of that green goo,” Lubnow said. “That means these two islands could eliminate 22,000 pounds of algae.”

He said the product has been used in other places for about a decade and has been successful. The pieces of floating plastic were initially guaranteed for 10 years, “but the original ones are still going, so the manufacturer now guarantees them for 15 years,” Lubnow said.

He said his company has set out similar islands at Duke Farms and in several lakes and ponds in Pennsylvania, where Princeton Hydro is working with the state’s parks department.

In a normal setting, the rafts are set out 50 to 75 feet from shore, but in Ashley Cove they are anchored next to the shoreline to give the lake’s fleet of weed harvesters room to maneuver since the cove is the off-loading place on the northern end of the lake.

The cove was also chosen since there is little circulation of water, so testing the effectiveness of the islands will be easier to measure.

The plants on the island include blue flag, rushes, sedges and milkweed.

“It’s interesting to see the islands out there with a haze of butterflies over them,” he said.

The plastic islands are strong enough to hold the plants but not strong enough to hold humans, so there’s little concern they will become swimming rafts.

The plastic will also hold up through the winter since the plants die back in the fall and rejuvenate in the spring.

The only concern is that the plants being grown are on the menu for Canada geese, so a screen of netting was set up to protect the seedlings.

“Once the plants get thick in there, the geese won’t climb on because they can’t see the ground,” Lubnow said. “We are leaving room around the edge for turtles to sun themselves, though.”

The original version of this story omitted an organization involved in the project. Though the Lake Hopatcong Commission received the grant, the Lake Hopatcong Foundation is implementing the grant and coordinated the floating wetland islands project.